1. Field of the Invention
The present invention relates to a slave cylinder for the operation of a friction clutch, especially in motor vehicles, with a housing, an inner portion, and an annular or cylindrical piston which is arranged between the housing and the inner portion. The friction clutch also includes a clutch release sleeve or clutch throwout sleeve or coupling socket joint which is in contact with the annular piston, and which clutch release sleeve can be axially displaced with respect to the housing, as well as a spring or pressure spring or compression spring. The spring is supported by both the clutch release sleeve and the housing, and the spring is secured against torsion.
2. Background Information
Such a slave cylinder is known from German Patent No. 41 09 125 A1, for example. In motor vehicles, the slave cylinder is interconnected to a master cylinder, which master cylinder is activated by means of the clutch pedal to operate the friction clutch. When pressure is applied to the slave cylinder, the annular piston arranged in said slave cylinder is displaced, which displacement presses the clutch release sleeve against the membrane spring of the clutch and disengages the clutch. In order to pre-stress the clutch release sleeve, it is loaded by the pressure spring. In this way, a portion of the disengagement path of the clutch release sleeve is preset, and an undefined reaction during operation is not possible. Said undefined reaction would be possible if the clutch release sleeve was able to move axially due to vibrations when the friction clutch was engaged, and would temporarily activate and deactivate. This would not only lead to a premature fatigue of the clutch release sleeve, but would also create noises which would reduce the comfort level, considering the increasing trend toward reducing driving noises. The slave cylinder according to the state of the art uses a coil spring as the pressure spring. Although this coil spring is principally secured against torsion, its elasticity leads to a relative movement of the bearing with respect to the housing when the clutch release sleeve activates against and loads the spring plate or spring collar. This movement, which occurs with each coupling process, on the one hand loads the pressure spring, which pressure spring must be made of high-quality material to have a sufficient life span. On the other hand, the pressure spring in slave cylinders is frequently shielded by a bellows-seal to keep grime and dust from entering between the clutch release sleeve and housing, or annular piston and housing, and cause premature wear and tear. However, a bellows-seal cannot withstand torsion and would be destroyed by it. For this reason, at least one of the ends of the bellows-spring must have a plain bearing or slide or sliding or friction bearing to adjust the relative movement between the clutch release sleeve and the housing. This required bearing not only makes the bellows-seal expensive to produce, but also makes great demands with respect to the seal, and particularly the sealed positioning of the plain bearing.
The increasing variety in the design of motor vehicles requires increasingly less space in the motor cavity. All aggregates and components must thus be designed as compactly as possible. For the pre-load stress exerted by the pressure spring to be sufficiently high on the one hand, but to achieve a spring characteristic that is as flat as possible on the other hand, the spring must have a sufficient number of turns and is thus long in construction. The length of the coil spring also defines the length of the slave cylinder.